Radiation-sensitive compositions are routinely used in the preparation of imagable materials including lithographic printing plate precursors. Such compositions generally include a radiation-sensitive component, an initiator system, and a binder, each of which has been the focus of research to provide various improvements in physical properties, imaging performance, and image characteristics.
Recent developments in the field of printing plate precursors concern the use of radiation-sensitive compositions that can be imaged by means of lasers or laser diodes, and more particularly, that can be imaged and/or developed on-press. Laser exposure does not require conventional silver halide graphic arts films as intermediate information carriers (or “masks”) since the lasers can be controlled directly by computers. High-performance lasers or laser-diodes that are used in commercially-available image-setters generally emit radiation having a wavelength of at least 700 nm, and thus the radiation-sensitive compositions are required to be sensitive in the near-infrared or infrared region of the electromagnetic spectrum. However, other useful radiation-sensitive compositions are designed for imaging with ultraviolet or visible radiation.
There are two possible ways of using radiation-sensitive compositions for the preparation of printing plates. For negative-working printing plates, exposed regions in the radiation-sensitive compositions are hardened and unexposed regions are washed off during development. For positive-working printing plates, the exposed regions are dissolved in a developer and the unexposed regions become an image.
Various radiation-sensitive compositions that can be used to generate free radicals upon thermal imaging and imagable elements containing same are described in numerous publications. Such negative-working imagable elements are generally processed after imaging using aqueous high pH developers. Development using gums is described for example, in EP Publications 1,751,625 (Van Damme et al. published as WO 2005/111727) 1,788,429 (Loccufier et al. et al.), 1,788,430 (Williamson et al.), 1,788,431 (Van Damme et al.), 1,788,434 (Van Damme et al.), 1,788,441 (Van Damme), 1,788,442 (Van Damme), 1,788,443 (Van Damme), 1,788,444 (Van Damme), and 1,788,450 (Van Damme), and WO 2007/057442 (Gries et al.). The imagable elements used in these references have either a protective oxygen-barrier overcoat, an intermediate layer between the substrate and imagable layer, or both.
The patent literature is full of teaching relating to various problems that the industry has been addressing for the last several decades, especially as “computer-to-plate” (CTP) imagable elements and equipment became prominent in the 1990's. Thus, there has been considerable efforts to develop positive-working elements with high imaging sensitivity (high photospeed), fast developability in various developing solutions (generally alkaline in pH), high resistance to degradation to pressroom chemicals (“chemical resistance”), plate durability, storage stability, high image stability, low environmental impact, and high run length.
Some of these problems have been solved by designing unique polymeric binders that are used in imagable layers to provide a matrix for the various imaging components. For example, U.S. Pat. No. 4,511,645 (Kioke et al.) describes the use of polymeric binders having unsaturated side chains in negative-working imagable elements to stabilize image formation. In addition, EP 0 924 570A1 (Fujimaki et al.) describes UV/visible-sensitive compositions and imagable elements containing polymeric binders having amido groups in side chains to increase alkaline solution solubility.
WO 2004/074930 (Baumann et al.) describes the use of polymeric binders having carboxylic acid side groups in combination with oxazole derivatives in UV-sensitive negative-working imagable elements. Such polymeric binders are also used with benzoxazole derivatives in UV-sensitive negative-working imagable elements, as described for example, in WO 2007/090550 (Strehmel et al.).
WO 2004/035687 (Loccufier et al.) describes the use of phenolic polymeric binders in positive- or negative-working imagable elements, which polymeric binders include a thio-linked heterocyclic group attached to the phenolic recurring units in order to increase the chemical resistance of the imagable layers. The heterocyclic groups can be any of a wide variety of sulfur, oxygen, or nitrogen-containing heterocyclic groups.
Copending and commonly assigned U.S. Ser. No. 11/949,810 (filed Dec. 4, 2007 by Baumann, Dwars, Strehmel, Simpson, Savariar-Hauck, and Hauck) describes the use of polymeric binder having pendant 1H-tetrazole groups in imagable elements that are processed using conventional alkaline developers.
Simple processing (development) of imaged elements has become a goal of workers in the lithographic art. For example, copending and commonly assigned U.S. Ser. No. 11/872,772 (filed Oct. 16, 2007 by K. Ray, Tao, Miller, Clark, and Roth) describes negative-working imagable elements that are sensitive to infrared radiation and can be simply processed (developed and “gummed”) using finishing gum solutions without the need for a conventional alkaline developer. This reduces the amount of processing equipment that is needed, costs, and consumption of processing solution.
In addition, copending and commonly assigned U.S. Ser. No. 11/947,817 (filed Dec. 4, 2007 by K. Ray, Tao, and Clark) describes the use of gums to develop imaged UV-sensitive, negative-working imagable elements that contain specific nonpolymeric diamide additives.
Copending and commonly assigned U.S. Ser. No. 12/017,408 (filed Jan. 22, 2008 by K. Ray and Kitson) describes the use of a single non-silicate processing solution to both develop and protect images in imaged positive-working lithographic printing plate precursors.
In addition, copending and commonly assigned U.S. Ser. No. 12/019,681 filed Jan. 25, 2008 by K. Ray and Kitson) describes the use of a “fresh” sample of processing solution to provide images in either positive-working or negative-working imagable elements.
U.S. Pat. No. 4,179,208 (Martino) describes a processing machine that uses an alkaline developer that is modified by the addition of a small amount of “gum”, and the developer is re-used or replenished but there are no details about the composition of this modified developer.